﻿/*
Copyright (C) 2006 Pedro Felzenszwalb

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
*/

#ifndef SEGMENT_GRAPH
#define SEGMENT_GRAPH

#include <algorithm>
#include <cmath>
#include "disjoint_set.h"

// threshold function
#define THRESHOLD(size, c) (c/size)

typedef struct {
    float w;
    int a, b;
} edge;

bool operator<(const edge &a, const edge &b)
{
    return a.w < b.w;
}

/*
* Segment a graph
*
* Returns a disjoint-set forest representing the segmentation.
*
* nu_vertices: number of vertices in graph.
* nu_edges: number of edges in graph
* edges: array of edges.
* c: constant for treshold function.
*/
universe *segment_graph(int nu_vertices, int nu_edges, edge *edges, float c)
{
    // sort edges by weight
    std::sort(edges, edges + nu_edges);

    // make a disjoint-set forest
    universe *u = new universe(nu_vertices);

    // init thresholds
    float *threshold = new float[nu_vertices];
    for (int i = 0; i < nu_vertices; i++)
        threshold[i] = THRESHOLD(1,c);

    // for each edge, in non-decreasing weight order...
    for (int i = 0; i < nu_edges; i++)
    {
        edge *pedge = &edges[i];

        // components conected by this edge
        int a = u->find(pedge->a);
        int b = u->find(pedge->b);
        if (a != b)
        {
            if ((pedge->w <= threshold[a]) &&(pedge->w <= threshold[b]))
            {
                u->join(a, b);
                a = u->find(a);
                threshold[a] = pedge->w + THRESHOLD(u->size(a), c);
            }
        }
    }

    // free up
    delete threshold;
    return u;
}

#endif
